Technical Field
Exemplary embodiment(s) of the present disclosure relate to articulated tugboat (tug) and barge (vessel) systems (ATB systems) and, more particularly, to a multi-functional powerhouse tug and barge (PTB) propulsion system for providing power, via a power-pack onboard the tug, to the barge.
Prior Art
A number of maritime companies around the world are virtually stuck with several vessels in their fleet that they can neither run nor be disposed. This is mainly because they are not economic to run or does/will not meet environmental compliance, though their overall structural condition may be quite good. These companies are spending thousands of dollars just to keep them in a berth where they are rotting day by day. These vessels need large investment to make them environmentally compliant to run in the developed world where regulatory requirements are quite stringent. Scrapping or writing off some of these vessels may make the financial statement for the company look bad. Selling them may be a competitive disadvantage if falls in wrong hand. Putting them back to service is the only way out.
The second motivation comes from the idea of developing a design concept for both existing retrofit and also for new designs by lowering crew requirement and yet achieving highest possible propulsive efficiency and operational flexibility. Self-propelled vessels need more crews compared to an unmanned vessel of the same cargo capacity. The best option is to find how to convert an existing self-propelled vessel into an unmanned vessel to reduce crewing cost and find a new concept of operating it in the most efficient way. Higher crew cost has already forced some companies switch to tug-barge system from regular self-propelled vessels.
The following are major operational costs comparison between self-propelled vessel and conventional tug-barge system. Standard major operational cost heads for a self-propelled vessel: Crew wage & benefits: 40 to 45%; and Fuel cost: 40 to 45%. Standard major operational cost heads for a tug & barge: Crew wage & benefits: 25 to 30%; and Fuel cost: 50 to 55%. One of the major problems with existing tug-barge system is their operational risk in rough seas compared to that of traditional vessels. The resulting downtime due to weather delays sometime outweighs the saving from smaller crew size.
From all the above considerations an economically viable option has to be thought about to convert these vessels or go for new construction where it will be easy to comply with continually changing regulatory and environmental requirements, as well as get quicker return on investment. For greater acceptability this concept will have to produce a highly flexible system for multi-purpose operational scenarios.
Issues with the Existing Vessels and their Configurations
The current configuration of a conventional tug-barge system includes a barge at the front, with a tug at an aft notch, connected by some sort of connection between them. The barge does not have any propulsion system and the tug with its propulsion system pushes the barge. FIG. 1 is a perspective view of a conventional barge 90 (prior art) employed in a conventional tug-barge system. There are a number of issues with this system: it needs an expensive and complicated notch at the stern of the barge which may cost huge initial investment. FIG. 2 is a perspective view of a conventional complicated notch 91 (prior art) on existing tug-barge system, which also needs a robust & complicated connection between the tug and barge, as smaller tug pushes large barge. This also a huge initial investment.
FIG. 3 is a perspective view of a conventional complicated articulation system 92 (prior art) in existing tug-barge system, which experiences a lack of propulsive efficiency due to highly non-streamlined transition between the tug and the barge causing added premium on operational cost. FIG. 4 is a perspective view of a conventional non-hydrodynamic transition interface 93 (prior art) between a tug & barge in conventional articulated tug-barge systems (ATB) and conventional integrated tug-barge systems (ITB), which has a smaller propulsive gears 95 option in the tug boat compared to that possible on the barge 94, again causing premium on operational cost from lower propulsive efficiency. See also FIGS. 5 and 5a (prior art).
FIG. 6 is a perspective view of a line-of-sight issue 96 in conventional ATB/ITB systems, which experience severe operational issue due to the line of sight from the tug's pilothouse over the barge, needing high pilothouse on the tug. Deck cargo even compounds this navigational and safety issue. FIG. 7 is a perspective view of a conventional tug 97 (prior art) with a high pilothouse and high center of gravity that becomes tender/unstable. The articulation system of such conventional tugs makes it difficult to operate at higher sea states, normally beyond sea state 3. Due to high pilothouse, the tug becomes very tender or unstable when separated from the barge. Therefore, it is difficult to keep continued compliance with changing environmental regulations. The tug-barge system has limited flexibility in operation due to its configuration etc.
Because of non-streamlined connection between the tug and barge in a conventional system, its propulsive efficiency is less than that of a similar sized ship, resulting in less speed for the same power used. Despite of all the advantages of a ship over a tug-barge system, the tug-barge system in most cases still proves to be more economical just because of its significantly smaller crew requirement. One of the great advantages of a tug-barge system is that the tug is readily replaceable with another one if their propulsion system fails. This is not in the case of a ship, where the propulsion engine failure virtually ceases its operation.
Accordingly, a need remains for a multi-functional tugboat in order to overcome at least one prior art shortcoming. The exemplary embodiment(s) satisfy such a need by providing that a multi-functional powerhouse tugboat employed in an ATB system that is convenient and easy to use, lightweight yet durable in design, versatile in its applications, and designed for providing power to the barge (vessel) via a power-pack onboard the tug. The primary modification achieved by removal of the accommodation and propulsion engines discussed above will convert a vessel into an unmanned carrier with no propulsion engine, just like a barge.